A. Field of the Invention
The invention relates to an adapter circuitry, especially to an external adapter circuitry for plugging into a printer port of a host computer for supporting computer telephony.
B. Description of the Prior Art
It is known that a MODEM is a circuit that uses digital data to modulate and demodulate a carrier wave so that digital data can be transmitted over an analog telephone network. The prior art technology uses a MODEM for supporting computer telephony for a host computer, including data transmission, facsimile, voice mail, call logging and even call blocking.
The first generation MODEM is a stand-alone device which communicates with a host computer via a serial communication port. There are two phone jacks residing on the circuit board of the MODEM for connecting to a telephone line and a telephone set. The circuit board of the MODEM contains a dedicated processor, usually a digital signal processor, for executing modulation/ demodulation, data computing, data processing and data permutation. It also has a power line for external power supply.
Since a digital signal processor is expensive, later development uses application software to replace a processor for a MODEM. It helps to reduce the cost of a MODEM and simplify the circuitry of a MODEM. Since the functionality of a MODEM will not be complete without application software, so the combination of a MODEM and its applicable software is then called "Software MODEM". Software MODEM is typically in the form of a circuit board that plugs into an internal slot of a host computer and communicates with the processor of the computer over a standard bus. It also has two phone jacks residing on the circuit board of the MODEM for connecting to a telephone line and a telephone set. It has no power line because the power supply directly comes from the host computer. The problem for the Software MODEM is that it is inconvenient to be installed. A user has to open the case of the host computer to plug the MODEM adapter card into the internal slot of the motherboard.
Due to the popularity of Internet communication, recently motherboard manufactures tend to build MODEM adapter card in the motherboard. Although this approach saves the installation trouble for the user, it creates another trouble for the motherboard manufacturers. The reason is that each country has its own communication system and standard for the communication device manufactures to follow. For this reason, each MODEM need to pass the examination of an authorized organization to obtain a certificate of that country before it can be sold to the market. Since the MODEM is now built in the motherboard, the motherboard manufacturers must deliver the entire motherboard to the authorized organization for examination. In this case, it would inevitably increase the cost of the motherboard manufacturers, including delivery, time and labor.